Topic Overview

Trapezius

Origin

• External occipital protuberance.

• Medial ⅓ of superior nuchal line.

• Ligamentum nuchae.

• Spinous processes of C7–T12 vertebrae.

Insertion

• Lateral ⅓ of clavicle.

• Acromion.

• Spine of scapula.

Nerve Supply

• Motor → Spinal accessory nerve (cranial nerve XI).

• Proprioceptive sensation → Ventral rami of C3, C4.

Actions

• Upper fibers → Elevate scapula.

• Middle fibers → Retract scapula.

• Lower fibers → Depress scapula.

• Upper + lower → Rotate scapula upward for overhead abduction (>90°).

Clinical Anatomy

• Accessory nerve injury (neck dissection, lymph node biopsy) → shoulder droop, difficulty shrugging.

• Weakness of upward abduction of arm.

Latissimus Dorsi

Origin

• Spinous processes of T7–L5.

• Thoracolumbar fascia.

• Iliac crest.

• Lower 3–4 ribs.

• Sometimes from inferior angle of scapula.

Insertion

• Floor of intertubercular sulcus (bicipital groove) of humerus.

Nerve Supply

• Thoracodorsal nerve (C6–C8).

Actions

• Extends, adducts, and medially rotates humerus.

• Powerful muscle in climbing, swimming, rowing.

• Raises trunk to arm (pull-ups).

Clinical Anatomy

• Used in flap surgery (muscle graft in breast reconstruction).

• Paralysis (thoracodorsal nerve injury) → difficulty climbing.

Dissection

Step 1: Skin Incision

• Midline incision from external occipital protuberance to sacrum.

• Transverse incisions across scapula and iliac crest.

• Reflect skin laterally.

Step 2: Expose Trapezius

• Identify trapezius in upper back (triangular sheet).

• Clean attachments from occipital bone, nuchal ligament, and spinous processes.

• Reflect laterally toward scapula.

• Beneath trapezius → identify accessory nerve and transverse cervical vessels.

Step 3: Expose Latissimus Dorsi

• Identify broad muscle in lower back.

• Clean attachments from thoracolumbar fascia, iliac crest, spinous processes, ribs.

• Reflect laterally toward humerus.

• Identify thoracodorsal nerve and vessels entering muscle.

Step 4: Demonstrations

• Contraction of trapezius → ask subject to shrug shoulders.

• Contraction of latissimus dorsi → ask subject to adduct/extend arm against resistance (as in climbing).